FIG. 1 is a view illustrating an RF front end in a TDD system. Since the RF front end shown in FIG. 1 does not operate a receiving end (Rx) in a transmission mode and does not operate a transmitting end (Tx) in a reception mode, the RF front end may be managed by a single antenna. However, the RF front end further requires a switch.
A power amplifier (PA) to increase output of the transmitting end (Tx) is mainly designed in a differential method, and a low noise amplifier (LNA) is also designed in the differential method to minimize common mode noise and ground effect in the RF front end module. Therefore, the RF front end further requires a balun as shown in FIG. 1.
A module that is manufactured by combining the switch and the baluns as shown in FIG. 1 is called an analog front end (AFE). In the multi-band or multi-mode wireless communication environment, the increase in manufacturing costs and system size of the AFE is becoming a problem.
To solve this problem of the AFE, a method for substituting this module with a chip has been suggested. Specifically, an RF switch with a complementary metal-oxide semiconductor (CMOS) transistor as shown in FIG. 2 is the representative method.
In the RF switch shown in FIG. 2, transistors are arranged such that a transmitting end (Tx) and a receiving end (Rx) are symmetric to each other. When “SW” is a high level, Ts2 is turned on and Tp2 is turned off, and the receiving end (Rx) is connected to an antenna. At this time, Ts1 is turned off at the transmitting end (Tx) and prevents signals from entering the transmitting end (Tx) from the antenna, and Tp1 is turned on and grounds the signals passing through Ts1, thereby guaranteeing isolation.
However, the transmission signal output from the transmitting end (Tx) is a high output signal that passes through the PA. Accordingly, linearity cannot be guaranteed while the signal passes through Ts1 which shows non-linearity with respect to the high output signal, and also, great loss may be caused.
In the case of the receiving end (Rx), the loss caused by Ts2 undermines the whole noise figure of the system.
Therefore, the RF switch shown in FIG. 2 guarantees high isolation, but causes side effects such as non-linearity and high insertion loss.